The Kawanishi H6K "Mavis" was a very large,
four-engine flying boat that saw action throughout the Second World War. It gave invaluable service
to the Imperial Japanese Navy thanks to its exceptional performance, becoming one of the
most relevant aircraft of the early Pacific War. During the 1920’s and early
30’s, Japan bought and copied a large number of western floatplanes and
flying boats. The Kawanishi company became specialized in creating them and developed
a relationship with the Short Brothers, a British manufacturer known for
making the same kind of aircraft. In 1933, Kawanishi had amassed enough experience
to make their own designs and tried to answer the Navy Experimental 8-Shi Large Flying
Boat Specification. While their attempt ultimately ended in failure, the Navy recognized
Kawanishi’s work by issuing the following year an exclusive specification. Named the 9-Shi,
it asked for a monoplane flying boat with: Following a visit to the Short Brothers company, a
team led by designers Yoshio Hashiguchi and Shizuo Kikuhara started working on the new project with
the internal designation of Type S. What emerged two years later was something quite unique.
The H6K, as it was named by the Japanese Navy, was a huge aircraft, being one of the largest
ever created up to that point. It had a parasol wing with a span of 40 m (131.23 ft) mounted above
the hull and supported by struts in a "v" shape. It had a crew of nine; a pilot, a co-pilot, a
radio operator, a flight engineer, a navigator, a bombardier, and three dedicated gunners. At first,
it was powered by four 840 hp (626 kW) Nakajima Hikari 2, nine-cylinder air-cooled radial engines.
Following its maiden flight on July 14, 1936, and during service trials, the H6K was found
to be slightly underpowered. This was soon corrected by reengining it with the Mitsubishi
Kinsei 43, a fourteen-cylinder air-cooled radial engine that could develop 1,000 hp (746 kW).
After passing the trials, the new aircraft entered service in January 1938 and
was officially designated the Navy Type 97 Flying Boat Model 1, or H6K1.
Full production followed, and the new units received the Model 2 or H6K2 designation
despite having only small internal equipment changes. In addition, two were converted to be
dedicated staff transports and were named H6K3. The Japanese flying boat saw action for
the first time in the Sino-Japanese war, where it was found to be the owner of an
exceptional range and endurance, great navigation qualities, and good stability in both
air and water. But some flaws were also evident, such as a slow cruising speed of around 130 mph
(209 km/h) or the fact that it was, even then, quite vulnerable. Outside the battlefield, it
proved to be complex to build and had a large production time. Some of these would become
major problems, as we’ll see further ahead. It wasn’t long until the
H6K4 variant, or Model 2-2, was around to try and counteract some of these
flaws. This became the H6K’s major production variant and was built from 1939 to 1942.
The K4 variant almost doubled the fuel capacity. Furthermore, the defensive armament was also
overhauled, with the addition of two "blisters" in the beam position bearing each a 7.7 mm (0.303
in) Type 92 machine gun. Two more Type 92 MGs could be found in an open bow position and in an
open dorsal one. But probably the most important addition brought by this variant was the single 20
mm (0.787 in) Type 99 cannon in the tail turret. Starting in August 1941, there was
also an engine change, with the 1,070 hp (798 kW) Kinsei 46 replacing the Kinsei 43.
When the Japanese hit Pearl Harbor, there were 66 H6K4s in frontline units of the Imperial
Japanese Navy, but, despite the scarcity in numbers, they played a very important
role in the initial Japanese advances. The "Mavis", as it was codenamed by the allies,
had a huge range with an absolute maximum value in excess of 6,000 kilometers (3,728 mi).
Although in practical terms, this distance was unlikely to be reached, let’s take a look at it.
6Ks is roughly the distance from Orlando, Florida to Anchorage, Alaska; from Lisbon, Portugal to
Dubai, United Arab Emirates; or, perhaps more fittingly, from Tokyo, Japan to Cairns, Australia.
Naturally, such good range was coupled with fantastic endurance, as the Mavis could spend
more than 26 hours in the air. In fact, 24-hour reconnaissance missions weren’t infrequent, and
to allow for those, it had sleeping quarters with two beds, a bathroom, and fresh water reserves.
The Mavis was incredibly well suited to performing recon missions in the vast oceanic expanses of
the Pacific Theater, but it wasn’t restricted to those. In the first year of the conflict, it
saw considerable use as a bomber, seeing that it could take up to 1,000 kg (2,205 lb) in bombs
or two 800 kg (1,764 lb) torpedoes. These were carried externally in the wing-supporting struts.
In addition, its large size also allowed it to carry a great variety of equipment, making it
quite good at navigating between islands and acting as a guide for ill-equipped aircraft. In
addition, the H6K’s powerful radio allowed it to relay messages from smaller recon airplanes
that would make reports outside of radio range. It also saw action in a variety of other
missions, such as transport and medevac. And so, it quickly became clear that there
weren’t quite enough of them in the Japanese Navy, a consequence of its lengthy production time.
However, this spell of success didn’t last forever, and it ended rather quickly when the
Japanese started encountering fiercer opposition. A clear example was when, on February 20,
1942, Task Force 11 approached Rabaul from the east intending on striking the recently
occupied Japanese base. In the morning, a Mavis discovered the American task force and
quickly reported its position, but, unknown to the Japanese crew, despite being 35 miles (56.3 km)
away, they were being identified by Lexington’s CXAM radar. This allowed the American carrier to
guide a pair of F4F Wildcat fighters led by the famous Lieutenant Commander John "Jimmy" Thach,
commanding officer of the VF-3 unit. His own words are a perfect description of what ensued.
"(...) There was a small opening in the cloud, and as I came into it, I looked down, and
not more than a thousand feet below was a huge wing with a red disk. It was my first
sight of an enemy aircraft as close as that, and it nearly scared me to death.”
Thatch made a run on the Japanese flying boat and it seems his aim was spot on.
"(...) The plane was almost completely engulfed in flames and it hit
the water with a huge explosion." The resulting flames could be seen from
Lexington’s deck more than thirty miles away. Half an hour later, another Mavis went down
in similar fashion, and just like that, in a very short period of time, Japan lost two
aircraft and 18 crewmen. That day would turn out to be catastrophic for the Japanese, with
nothing less than 15 brand new G4M1 "Betty" bombers shot down by Lexington’s fighters, but
that episode is beyond the scope of this video. Remaining on the Mavis topic, it’s easy to
explain the huge explosions since, much like almost all Japanese aircraft of the time, the H6K
was unarmored and lacked self-sealing fuel tanks. Its defensive armament was also quite weak, with
the four rifle-caliber machine guns amounting to very little. Only the 20 mm cannon in the
rear turret would give pause to an American pilot flying an Wildcat fighter. In addition, as
shown by this picture of a declassified Technical Air Intelligence Center report, the Americans
soon found that the Mavis had no defenses in the 3 and 9 o’clock bearings, above and below.
The H6K5, a new variant with the more powerful Mitsubishi Kinsei 51 or 53 engines rated at 1,300
hp (969 kW), did little to change the situation, and toward the end of 1942, the Mavis was
gradually pulled away from the frontlines, giving way to the much tougher H8K Emily.
But its retirement as a frontline aircraft wasn't the end of the line. In fact, it saw action
until the last days of the war, now as a dedicated transport. Beyond the H6K3, it had two other
transport variants, the H6K2-L and 4-L, of which 36 were built. These had all armament removed,
increased fuel capacity, cargo compartments ahead of the cockpit and in the far back, a galley
behind the cockpit, a mid-ship cabin with 8 seats or 4 beds, and an aft cabin with 10 seats more,
taking the passenger limit to a maximum of 18. Beyond the Navy, these transport variants also
saw civilian use by the Greater Japan Air Lines. All in all, 215 Mavis of all variants were
produced, but only a handful survived the war. The Mavis, much like many other Japanese
aircraft, achieved its wonderful performance by sacrificing resilience. As such, it was a truly
remarkable aircraft from a civilian perspective, but due to its vulnerabilities, a
less than ideal combat aircraft. Why such an assessment if other Japanese aircraft,
like the acclaimed A6M Zero fighter, suffered from exactly the same flaw? Well, the Zero was small,
fast, and agile, and, in the end, one going down meant losing one pilot. The Mavis was very large,
slow, and cumbersome and was costing nine crewmen at a time, something Japan couldn’t afford.
But the Japanese Navy did learn, and the Mavis’ successor, the H8K Emily,
was armored and had self-sealing fuel tanks, making it much more difficult to shoot down.
In fact, the Emily can be considered one of the best flying boats of the war.
Beyond the military outlook, the Mavis was a unique and beautiful aircraft.
Do you agree? What is your favorite flying boat? Let me know in the comments below!
Thank you very much for watching.
